1. Field of the Invention
The present invention relates to a technique for manufacturing a piezoelectric (electrostrictive) actuator functioning as an ink-expelling drive source for an ink-jet type recording head, and particularly to a technique for manufacturing a piezoelectric actuator obtained using an application method.
2. Description of the Related Art
Piezoelectric actuators functioning as electromechanical conversion elements comprise piezoelectric films sandwiched between upper and lower electrodes. These actuators are used for the ink-expelling drive sources of ink-jet type recording heads, as well as solid-element motors, relays, switches, filters, and the like. The piezoelectric films constituting such piezoelectric actuators are formed from lead zirconate titanate (Pb(Zr, Ti)O3) and other PZT-based piezoelectric materials, or from piezoelectric/electrostrictive materials obtained by adding oxides of niobium, nickel, magnesium, or other metals to these systems. Piezoelectric films demonstrate an inverse piezoelectric effect, which is induced when an electric field is applied, making it possible to create deformation in piezoelectric actuators and to perform drive control on a submicron scale.
For example, the printing method disclosed in Japanese Patent Laid-open No. H3-128681 is known as a technique for forming such piezoelectric films. This printing method is a technique for obtaining piezoelectric films by forming a film on the desired substrate using a paste or slurry containing piezoelectric (electrostrictive) ceramic particles as its principal component, and heat-treating the resulting film. Using this printing method makes it easier to employ lithographic techniques or mechanical processing techniques such as laser processing or slicing, and allows any piezoelectric film configuration to be designed. Integration density of piezoelectric actuators can also be improved due to a greater variety of design options.
When, however, a piezoelectric actuator is fabricated by the printing method in accordance with the aforementioned Japanese Patent Laid-open No. H3-128681, the following problems are encountered because of the need to keep the atmosphere at 800 to 1000xc2x0 C. during the heat treatment (sintering of piezoelectric film precursors). First, residual stress acts during the formation of a piezoelectric film, facilitating crack initiation and making it more difficult to obtain thicker piezoelectric films. Second, the piezoelectric characteristics of piezoelectric actuators vary because the high-temperature heat treatment vaporizes the lead in the piezoelectric film precursors and changes the stoichiometric ratio of the piezoelectric films. In addition, the lead diffuses in, or otherwise affects, the lower electrode, bringing about a reduction in the withstand voltage of the piezoelectric actuators and creating other problems.
Thicker piezoelectric films should be used to make piezoelectric actuators more reliable. It is also desirable that the piezoelectric actuators be fabricated in a low-temperature environment in order to maintain the same piezoelectric film composition and to prevent lead from being vaporized by the heat treatment.
In addition, Japanese Patent Laid-open No. H9-157019 describes obtaining complex oxide films through the use of materials prepared by adding complex oxide powders and complex oxide sols to solvents. No reference is made in this publication, however, to the type of composition used for such complex oxide sols.
With the foregoing in view, it is an object of the present invention to fabricate a piezoelectric actuator by an application method in a low-temperature environment and to make it possible to obtain a thicker piezoelectric film. Another object is to provide a highly practical piezoelectric film by combining the advantages of a plurality of material types. Yet another object is to provide a piezoelectric actuator equipped with such a piezoelectric film, to provide an ink-jet type recording head and ink-jet printer equipped with this piezoelectric actuator, and to provide a method for manufacturing these.
The piezoelectric actuator of the present invention is a piezoelectric actuator comprising a stacked structure consisting of a top electrode, a piezoelectric film, and a bottom electrode, wherein the piezoelectric film comprises a first group at piezoelectric ceramic particles and a second group of piezoelectric ceramic particles; the particles constituting the first group of piezoelectric ceramic particles are larger than the particles constituting the second group of piezoelectric ceramic particles; and the first group of piezoelectric ceramic particles and second group of piezoelectric ceramic particles have different compositions.
The fact that the first group of piezoelectric ceramic particles and the second group of piezoelectric ceramic particles have different compositions makes it possible to obtain a piezoelectric actuator whose composition combines the advantages of both.
The first group of piezoelectric ceramic particles should preferably be composed of a material whose piezoelectric constant is higher than that of the second group of piezoelectric ceramic particles.
Adequate piezoelectric characteristics of the film as a whole can be obtained because the first group of piezoelectric ceramic particles (large particles) have a high piezoelectric constant.
The second group of piezoelectric ceramic particles should preferably be composed of a material having higher plasticity than the first group of piezoelectric ceramic particles.
A piezoelectric film having high plasticity overall can be obtained because of the high plasticity of the second group of piezoelectric ceramic particles.
The plasticity of film or bulk can be evaluated by Young""s modulus as physical or mechanical characteristics. Material having low Young""s modulus is soft and has a high plasticity. To measure Young""s modulus of thin film having a micron scale thickness, we can use nano-indentor (n-indentor). To measure Young""s modulus of thick material such as bulk, we can use a cantilever.
Young""s modulus is, for example, 70-100 GPa (gigapascal) for PZT, 10-20 GPa for PMN-PZT. Material having low Young""s modulus and high plasticity has advantages such as hardness to break when applying external force (stress) and easiness to make thick films. On the other hand, if the material is too soft (i.e. Young""s modulus is too low), the film cannot efficiently transmit a mechanical force. In other words, the film absorbs the force due to a large elasticity.
This invention may, by combination of crystal with high Young""s modulus and crystal with low Young""s modulus, flexibly control the properties of the films.
The particle size of the first group of piezoelectric ceramic particles should preferably be from 0.2 xcexcm to less than 10 xcexcm. This is because the piezoelectric film has inadequate piezoelectric characteristics when the size is less than 0.2 xcexcm, whereas using particles measuring 10 xcexcm or greater makes the irregularities on the surface of the piezoelectric film more pronounced and has an adverse effect on the reliability of the piezoelectric film. In addition, the particle size of the second group of piezoelectric ceramic particles should preferably be from 10 nm to less than 100 nm. Furthermore, the thickness of the piezoelectric film should preferably be from 2 xcexcm to 100 xcexcm.
The composition of the piezoelectric ceramic particles constituting the first group of piezoelectric ceramic particles or the second group of piezoelectric ceramic particles may be any of the following: lead titanate (PbTiO3), lead zirconate titanate (Pb(Zr,Ti)O3), lead zirconate (Pb ZrO3), lead lanthanum titanate ((Pb, La), TiO3), lead lanthanum zirconate titanate ((Pb, La) (Zr, Ti)O3), lead zirconate titanate magnesium niobate (Pb(Zr, Ti) (Mg, Nb)O3), Pb(Ni, Nb)O3xe2x80x94Pb(Zr, Ti)O3 (PNN-PZT), or a material obtained by adding any two elements selected. from W, Ni, Mn, Zn, and Co to lead zirconate titanate.
The composition of the first group of piezoelectric ceramic particles should preferably be any of the following; lead zirconate titanate (Pb(Zr, Ti)O3; PZT), lead lanthanum zirconate titanate ((Pb, La)(Zr, Ti)O3), barium titanate (BaTiO3), or lead nickel niobate zirconate titanate (Pb(Ni, Nb)O3xe2x80x94Pb(Zr, Ti)O3: PNN-PZT). This is because PZT and the other materials in the first group have good piezoelectric characteristics.
The composition of the second group of piezoelectric ceramic particles may be any of the following: lead magnesium niobate zirconate titanate (Pb(Mg, Nb)(Zr, Ti)O3: PMN-PZT), potassium niobate tantalate (K(Nb, Ta)O3), or bismuth.sodium titanate (Bi, Na)TiO3. This is because PMN-PZT and the other Materials in the second groups are characterized by consisting of small particles and having excellent plasticity.
The ink-jet type recording head of the present invention comprises a pressure chamber substrate for providing chambers, and the piezoelectric actuator of the present invention, in which pressure chambers are formed at positions in which pressurization is possible.
The ink-jet printer of the present invention comprises the ink-jet type recording head of the present invention.
The method for manufacturing a piezoelectric actuator in accordance with the present invention comprises an application step in which a piezoelectric film precursor obtained by mixing piezoelectric ceramic particles and an amorphous composite oxide whose composition is different from that of the particles is formed into a film of prescribed thickness by an application method, and a crystallization step in which the piezoelectric film precursor is hydrothermally treated under constant conditions, and the piezoelectric film precursor is crystallized.
The piezoelectric ceramic particles should preferably be composed of a material whose piezoelectric constant is higher than that of the crystallized amorphous composite oxide.
In addition, the crystallized amorphous composite oxide should preferably have higher plasticity than the piezoelectric ceramic particles.
The composition of the piezoelectric ceramic particles may be any of the following: lead zirconate titanate (Pb(Zr, Ti)O3: PZT), lead lanthanum zirconate titanate ((Pb, La)(Zr, Ti)O3), barium titanate (BaTiO3) or lead nickel niobate zirconate titanate (Pb(Ni, Nb)O3xe2x80x94Pb(Zr, Ti)O3: PNN-PZT).
The composition of the amorphous composite oxide may be any of the following: lead magnesium niobate zirconate titanate (Pb(Mg, Nb)(Zr, Ti)O3: PMN-PZT), potassium niobate tantalate (K(Nb, Ta)O3), or bismuth sodium titanate (Bi, Na)TiO3.
The size of the piezoelectric ceramic particles is characterized by ranging from 0.2xcexc to less than 10 xcexcm. The amorphous portion of the piezoelectric film precursor is characterized by growing into piezoelectric ceramic particles measuring from 10 nm to less than 100 nm in the crystallization step.
The temperature of the entire manufacturing process is lower than that of a conventional manufacturing method because the aforementioned process allows the piezoelectric film precursor formed by the application method to be crystallized by a hydrothermal treatment. The thickness of the piezoelectric film precursor can be set from 2 xcexcm to less than 100 xcexcm by admixing piezoelectric ceramic particles into the piezoelectric film precursor.
To maintain constant conditions during the hydrothermal treatment, the treatment solution should preferably be a barium hydroxide aqueous solution, a lead hydroxide aqueous solution, or a mixture thereof, adjusted to a concentration of 0.05 M to 2.0 M. In addition, the treatment temperature should preferably be kept within a temperature range of 120xc2x0 C. to 200xc2x0 C. Furthermore, the treatment pressure should preferably be kept constant at between 2 atm and 10 atm, and the treatment time should be set to between 10 minutes and 120 minutes.
The method for manufacturing an ink-jet type recording head in accordance with the present invention comprises a step of processing a substrate to form pressure chambers, and a step of manufacturing a piezoelectric actuator at positions in which the pressure chambers can be pressurized, by the method for manufacturing a piezoelectric actuator in accordance with the present invention.